Sliding window manufacturers typically use locking devices on the sash meeting rails to provide environmental control and security and to prevent unintentional opening of their windows. Typical locking devices help provide forced-entry resistance (FER) as a means to prevent unintended opening of the window.
Testing for forced-entry resistance (per ASTM F588) typically involves applying increasing opposing loads to the upper and lower sashes of the window in both horizontal and vertical directions and manipulating the window hardware for a specified period of time with simple hand tools such as a putty knife and/or a piece of stiff steel wire to try to gain access. Grading, which runs from 10 to 40, corresponds to increasing applied loads and manipulation times, with a minimum of grade 10 normally expected.
Failure of window hardware during the FER manipulation portion of testing typically occurs when the cam or lever handle is accessed and rotated to the unlocked position to allow unintended opening of the window. Typical locking devices use various means to help prevent FER manipulation of the lock's cam and lever handle. Some examples include; pick plates which extend under the bottom surface of the cam, shrouded keepers to help prevent access to the lock handle, stiff detents in the locked position, and locking “buttons” to help prevent the handle or cam from being rotated. One example of a prior sliding window lock device providing FER is disclosed in U.S. Patent Publication No. 2008/0169658 A1, owned by the owners of the present invention, and hereby fully incorporated herein by reference.
These methods generally work well independently or in combination with each other but typically add cost to the product due to the extra components required in the lock assembly to achieve FER manipulation protection. What is needed are improved lock devices and methods to prevent FER manipulation of the lock which do not require additional components (a passive FER system) compared to a non-FER lock assembly.